Clamping device



Oct. 28, 1952 D. H. STENT CLAMPING DEVICE 2 Sl-lEETS-SHEET 1 Original Filed Dec. 19, 1947 was;

wow! H. STENT AffokNEY Oct. 28, 1952 D. H. STENT 2,615,678

' CLAMPING DEVICE Original Filed Dec. 19, 1947 2 Sl-lEETS-Sl-IEET 2 e Fm x3 DUDLEY H. STENT Patented Oct. 28, 1952 CLAMPING DEVICE Dudley H. Stent, Westminster, London, England, assignor to Stent Precast Concrete Limited,

London, England Continuation of abandoned application Serial No.

792,639,.December 19, 1947.

This application September 19, 1950, Serial No. 185,659. In Great Britain October 13, 1943 Sectionl, Public Law 690, August 8, 1946 Patent expires October 13,. 1963 8 Claims.

This application is a continuation of my .pending application, Serial No. 792,639,1'iled December 19, 1947, now abandoned.

This. inventionrelates to a clamping device particularly adapted for use in applying tension to wires, rods and the like in the molding of pre- '.To effect the stretching of the reinforcements and to anchor them in the end portionsof the concrete, it has already been proposed to Wrap the reinforcements around rigid transverse devices, such as'bars, situated at the two ends of the concrete, the reinforcements being stretched by increasing the distance between the'two transverse devices.

For the above purpose, according to the invention, one or both end portions of a stretched Wire or rod reinforcement for a pro-stressed concrete article and enwrapping a rigid transverse member, is clamped between such enwrapped member and a surface on means stretching the reinforcement. Thus the means which stretches or maintains the reinforcement stretched, nips the end portion of. thereinforcement and precludes the latter slippingand unwrapping off the transverse member.

For example, a reinforcement wire formed into a loop enwraps the outwardly directed convex surface of a stout transverse cleat bar of halfround cross section located within one or both ends of the mold for the concrete, the wire, for instance, extending threetimes between the two transverse bars and terminating at each. Each end portion of the wire, after enwrapping the convex surface of the respective transverse bar, extends between the inwardly directed flat surface of the respective. transverse bar and a washer or plate behind a nut on the stem of a bolt extending freely through the transverse bar-and the respective end of the mold. Tension maintained on the wire by the bolts at both ends of the mold alsoclamps the ends of the wire between the respective washers or plates and the respective transverse bars.

.. An. object of thisinvention .is to provide, in

concrete molding or other. apparatus, -aijoint comprising an element for receiving tension, a tensioning member and a clamping part, wherein the element is wrapped about a first surfaceof the tensioning member and then is clamped against a second surface of the member by the clamping part, the clamping action being transmitted through the-member by the actual 'tensioning force.

Another object is to provide a joint for simultaneously pro-stressing two or more reinforcing rods, in which the joint includes a cylindrical bolt passed through a hole in the tensioning member and clampin part, the hole being tapered in the direction of the tension force. This arrangement permits rocking of the tensioning member, thereby compensating for unequal dimensions of the two reinforcing rods.

Another object of the invention is to provide a device for simultaneously gripping and applying a tensioning force to at least one elongated element comprising a tensioning member having a first surface of substantial area facing in the direction of the tensioning force for engaging a first portion of .each said elongated element. and having a second oppositely facing surface of substantial area for engaging a second portion of said elongated element, a clamping part located in proximity to said second surface and in contact with. said second portion, and means for exerting tensioning force on said clamping part to compress said second portion between said part and .said member while simultaneously applying tensioning force to the first portion of said elongated elementthrough the first surface of said member.

Still another'object of the invention is to provide a device for simultaneously gripping and applying a tensioning force to at least one elongated element comprising a tensioning member about which said element is enwrapped, said member having a first surface area facing in the direction of the tensioning force for engaging a first portion of each said elongated element, and having a second oppositely facing surface of substantial area for engaging asecond portion of said elongated element, said element passing firstabout saidfirst surface and then along said second surface, a clamping part located in proxmember while simultaneously applying tension- ;ing forceto the first portion-of. said;v elongated elementthrough the first surface of said member.

A further object is to provide a joint for securing and applying tension to rods which are positioned asymmetrically on the tensioning member without causing bending movements in the joint.

These and other objects will become apparent from a consideration of the accompanying drawings in which:

Fig. 1 is a broken longitudinal section of a mold for concrete provided with means for stretching longitudinal reinforcements for the concrete, and

Fig. 2 is a corresponding plan.

Fig. 3 is a view similar to Fig. 1 but showing a modification.

Fig. 4 is a longitudinal section of an end of a mold showing a modification.

Figs. 5 and 6 are longitudinal sections on a larger scale of alternative clamping devices for the wire reinforcement.

Referring more particularly to Figs. 1 and 2, a is a mold, for concrete which is to be compressively pre-stressed, by embedding wires b, which are maintained stretched in the mold a whilst the concrete is setting.

To stretch the wires b, they are bent to enwrap transverse cleat bars 0 of half-round cross section located one at each end of the mold and drawn apart so as to stretch the wires b extending between them. The transverse bars 0 are each mounted on a longitudinal bolt d extending freely therethrough and through the respective end wall a of the mold a. The wires b are stretched by hydraulic rams e thrusting against a crosshead f through which the bolts (1 at one end of the mold extend to terminate with heads 11 on the outer face of the crosshead I. When the wires b have been stretched by the rams e, the tension on the wires b is maintained by tightening up nuts 0 on the bolts d.

To prevent the wires b slipping from enwrapping the bars 0, the ends of each wire b enwrapping a bar 0, are clamped between the latter and a washer plate h, interposed between the flat surface of the respective bar 0, and a nut i on the bolt 11 and transmitting to the wires b the tension applied by the bolt 11.

In the example shown in Figs. 1 and 2, there are four wires b in the mold a, with two bolts d and two cross bars 0 at each end of the mold a, one wire being on each side of each bolt d. Also these wires b extend once above and once below the cross bars 0, so that both ends of each wire b are at the same end of the mold a.

In the arrangement shown in Fig. 3, each wire b extends three times between the two ends of the mold, so that of each wire b there are two lengths above the bolts d and one length beneath, and also the ends of each wire b are at opposite ends of the mold a. To distribute the tension equally between the single length of wire beneath the bolt and the double length of wire above the bolt, the bolts d are set so as to extend through the cross bars 0 nearer to the double lengths of wire than to the single length of wire.

As shown in Fig. 4, the cross bars 0 instead of being of half-round cross section, may be of crescent or semi-tubular cross section and the washer plate It may be of half-round cross section, the end of the wire 17 being clamped between the opposed rounded concave surface of the cross bar 0 and the convex surface of the washer plate h.

The wires b to be stretched are pre-bent to the looped shape necessary to fit on and between the cross bars 0, and with the aid of a suitable jig can all usually be bent to the same length with only a very slight probable difference between all the wires of a set. To take up and equalize any such small difference in length between wires on opposite sides of opposed bolts d, the holes for the bolts in the cross bars 0 are tapered inwardly towards the nuts 1 as shown in Figs. 5 and 6, so that the cross bars 0 are capable of rocking.

The washer plates it may bend in exerting the clamping action on the ends of the wires b. To prevent in such case the clamping effect being diminished or ineffective on the outer of two wire ends b, the surface of the cross bars c can be grooved to take both of the two wire ends on convergent surfaces of the groove and projecting from the groove 7', as shown in Fig. 5. The two wire ends b will automatically mutually displace one another so as to be equally clamped notwithstanding any bending of the washer plate 71..

After the concrete has set, the bolts d are unscrewed from the nuts 2 and removed. The holes thereby left in the concrete can be plugged with wet concrete.

What is shown as a transverse bar in the drawings can be developed into other shapes. For instance for stretching wires in pre-stressed concrete articles of substantially round cross section, such as hollow piles and poles, the bar may be a ring.

It is not essential that the wire stretching arrangement consisting of the bars 0 and bolts d shall be located within the mold. They can be located outside the ends of the mold. In such case the wires are cut at the ends of the set concrete.

Instead of casting the concrete or all of the concrete around the stretched reinforcements, one or more pre-cast concrete units may be inserted between the anchoring devices and strut them apart on partial release of the stretched reinforce ment, the pre-formed concrete strut bearing against and causing the washer plate still to nip the wire reinforcement. Such pre-formed concrete struts may be more or less tubular and more or less surround the stretched reinforcements. The struts are inserted dry and may be amplified by added wet concrete or grouting embedding the stretched reinforcements.

The concrete units, whether cast around the stretched reinforcements or inserted dry as precast units, may be arranged so that when the concrete has set or, if pre-cast, when in position, straining bolts and nuts can be recovered. Cavities thus exposed can be plugged with wet concrete.

The invention is equally pplicable to concrete units which are pre-stressed by means of high tensile steel subjected to an initial tension substantially greater than or equal to the elastic limit of normal mild steel, or to concrete units which are pre-stressed by means of ordinary mild steel.

In a general manner, while I have, in the above description, disclosed what I deem to be practical and efficient embodiment of my invention, it should be well understood that I do not wish to be limited thereto as there might be changes made in the arrangement, disposition and form of the device without departing from the principle of the present invention as comprehended within the scope of the accompanyin claims.

It is further to be understood that the joint and the clamping and tensioning device have numerous applications outside of the molding of prestressed concrete objects.

I claim:

1. A device for simultaneously gripping and applying a tensioning force to at least one elongated element, comprising a tensioning member having a first surface of substantial area facing in the direction of the tensioning force for engaging a first portion of each said elongated element and having a second oppositely facing surface of substantial area for engaging a second portion of said elongated element, a clamping part located in proximity to said second surface for contact with said second portion, and means for exerting tensioning force on said clamping part to compress said second portion between said part and said member While simultaneously applying tensioning force to the first portion of said elongated element through the first surface of said member.

2. A device for simultaneously gripping and applying a tensioning force to at least one elongated element, comprising a tensioning member about which said element is enwrapped, said member having a first surface area facing in the direction of the tensioning force for engaging a first portion of each said elongated element and having a second oppositely facing surface of substantial area for engaging a second portion of said elongated element, said element passing first about said first surface and then along said second surface, a clamping part located in proximity to said second surface and in contact with said second portion, and means for exerting tensioning force on said clamping part to compress said second portion between said part and said member while simultaneously applying tensioning force to the first portion of said elongated element through the first surface of said member.

3. A device according to claim 2, said member and said part having matching openings therein, said second surface of said member including two areas located on opposite sides of the opening in said tensioning member, said means for exerting tensioning force consisting of a cylindrical force transmitting member passing through said openings and means carried by said cylindrical member for engaging and transmitting force to said clamping part, the walls of the opening in said tensioning member being diverging in the direction of application of the tensioning force to permit rocking of said tensioning member to compensate for small differences in the dimensions of the elements in contact with said second portion of said member.

4. A device according to claim 3, in which the two areas forming said second surface of the tensioning member comprise grooves having tapering walls.

5. A device according to claim 2, said member and said part having matching openings therein,

said means for exerting tensioning force consisting of a cylindrical force transmitting member passing through said openings and means carried by said cylindrical member for engaging and transmitting force to said part.

6. A device according to claim 5, there being a plurality of said elongated elements disposed unsymmetrically with regard to said member so as to apply an unbalanced load to said member, said matching openings and said cylindrical member being located off center with respect to said tensioning member in the direction of the greatest load on said member.

7. A device according to claim 2, in which said member is arcuate in cross section, the outer convexly curved surface forming said first surface and the inner concavely curved surface forming said second surface, said clamping part having a surface configuration matching said inner surface, said member and said part having matched openings therein, said means for exerting tensioning force consisting of a cylindrical force transmitting member passing through said openings and means carried by said cylindrical member for engaging and transmitting force to said part.

8. In the art of molding pre-stressed concrete having at least one elongated element under tension molded therein, a novel device for simultaneously gripping and applying tensioning force to such elongated element, said device comprising a tensioning member having a first and convex surface of substantial area facing in the direction of the tensioning force for engagement by a first portion of said element spaced from the end of the element, and having a second surface of substantia1 area facing oppositely to said first surface for engagement by a second portion of element nearer the end thereof than said first portion, thereby providing enwrapping of the element about said member, a clamping part having a surface of a configuration similar to that of said second surface, and tensioning means engaging said clamping part to pull said clamping part toward the second surface of said member to clamp said second portion of said elongated element between said member and said clamping part while simultaneously urging said member in the direction of the tensioning force to apply tension to said element through said first surface.

DUDLEY H. STEN'I'.

REFERENCES CITED UNITED STATES PATENTS Name Date Haas Oct. 26, 1909 Number 

